1. D. Tilman, J. Knops, E. Siemann, Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108, USA.
2. D. Wedin, Department of Botany, University of Toronto, Toronto, Ontario, M5S 3B2, Canada.
3. P. Reich, Department of Forest Resources, University of Minnesota, St. Paul, MN 55108, USA.
4. M. Ritchie, Department of Fisheries and Wildlife, Utah State University, Logan, UT 84322, USA.